An agricultural harvester known as a “combine” is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating, and cleaning. A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing rotor. The threshing rotor rotates within a perforated housing, which may be in the form of adjustable concaves, and performs a threshing operation on the crop to remove the grain. Once the grain is threshed it falls through perforations in the concaves onto a grain pan. From the grain pan the grain is cleaned using a cleaning system, and is then transported to a grain tank onboard the combine. A cleaning fan blows air through the sieves to discharge chaff and other debris toward the rear of the combine. Non-grain crop material such as straw from the threshing section proceeds through a residue handling system, which may utilize a straw chopper to process the non-grain material and direct it out the rear of the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, such as a semi-trailer, gravity box, straight truck, or the like, and an unloading system on the combine is actuated to transfer the grain into the vehicle.
More particularly, a rotary threshing or separating system includes one or more rotors that can extend axially (front to rear) or transversely within the body of the combine, and which are partially or fully surrounded by a perforated concave. The crop material is threshed and separated by the rotation of the rotor within the concave. Coarser non-grain crop material such as stalks and leaves pass through a straw beater to remove any remaining grains, and then are transported to the rear of the combine and discharged back to the field. The separated grain, together with some finer non-grain crop material such as chaff, dust, straw, and other crop residue are discharged through the concaves and fall onto a grain pan where they are transported to a cleaning system. Alternatively, the grain and finer non-grain crop material may also fall directly onto the cleaning system itself.
A cleaning system further separates the grain from non-grain crop material, and typically includes a fan directing an airflow stream upwardly and rearwardly through vertically arranged sieves which oscillate in a fore and aft manner. The airflow stream lifts and carries the lighter non-grain crop material towards the rear end of the combine for discharge to the field. Clean grain, being heavier, and larger pieces of non-grain crop material, which are not carried away by the airflow stream, fall onto a surface of an upper sieve (also known as a chaffer sieve), where some or all of the clean grain passes through to a lower sieve (also known as a cleaning sieve). Grain and non-grain crop material remaining on the upper and lower sieves are physically separated by the reciprocating action of the sieves as the material moves rearwardly. Any grain and/or non-grain crop material remaining on the top surface of the upper sieve are discharged at the rear of the combine. Grain falling through the lower sieve lands on a bottom pan of the cleaning system, where it is conveyed forwardly toward a clean grain auger. The clean grain auger conveys the grain to a grain elevator, which transports the grain upwards to a grain tank for temporary storage. The grain accumulates to the point where the grain tank is full and is discharged to an adjacent vehicle such as a semi trailer, gravity box, straight truck or the like by an unloading system on the combine that is actuated to transfer grain into the vehicle.
In order to measure the mass flow rate of clean grain entering the grain tank from the grain elevator of a combine, it is known to provide a grain mass flow sensor. Often, the grain mass flow sensor involves a sensor plate located at or near the outlet of the grain elevator. The grain elevator generally includes a long drive chain loop that extends vertically from the outlet of the clean grain auger near the bottom of the combine to the grain tank near the top of the combine, having paddles attached to certain of the chain links. Grain is carried upwards on the paddles and then flung outwardly towards the outlet of the grain elevator as the drive chain loop passes over the uppermost sprocket, where the sensor plate is located. As the velocity of the grain exiting the grain elevator may be known, the reaction force of the grain striking the sensor plate is then used to calculate the mass flow rate of grain entering the grain tank. This information may be used by other systems to calculate the yield, for example at various locations in a field.
Various difficulties arise from the use of a sensor plate type grain mass flow sensor. The grain to be measured may vary in bulk properties like moisture, coefficient of friction, coefficient of restitution, and cohesiveness as non-limiting and often crop, temperature, and humidity dependent examples. The grain mass flow sensor must function reliably and accurately in a machine that is operated off-road in fields that may be rough, uneven, and sloped, so that incline and vibration may affect the signals produced by the sensor. Further, the grain mass flow sensor, and all of its subcomponents, must operate in a dusty abrasive environment in the presence of moisture and temperature variations, and must be durable and robust during assembly and subsequent maintenance.
Prior art installations of grain mass flow sensors used in conjunction with grain elevators suffered further from the fact that grain flow proceeding from the grain elevator exit often did so in a relatively uncontrolled fashion. Rather than a coherent flow of grain impacting the sensor plate, the flow of grain was scattered so that some of the grain moved on a trajectory towards the sensor plate, and some of the grain moved on an oblique trajectory relative to the sensor plate. As a consequence, the relation between the grain flow and the mass flow sensor signal tended to be non-linear. Prior art installations of grain mass flow sensors also tended to produce imprecise results due to the variation in bulk properties of the grain, due to changes in incline of the combine, due to vibration, due to drift of the load cell output, and due to the high range of measurements involved.
Certain prior art references have addressed one or more of these problems individually, but none have fully addressed all of the problems. U.S. Pat. Nos. 5,736,652 and 5,970,802 provide a curved sensor plate that compensates for variations in the frictional properties of the grain. However, the sensors used are torsional in nature, relying on springs or counterweights to provide the reaction force and upon a tangential displacement sensor. Such torsional arrangements have been determined not to be sufficiently robust to endure the harsh environment, and are susceptible to greater output variation due to changes in incline or vibrations, which must be compensated to a greater degree using inclinometers. Alternately, U.S. Pat. Nos. 5,736,652 and 5,970,802 utilize multi-point sensor arrangements unsuitable for use near the grain elevator exit. U.S. Pat. No. 5,343,761 uses a moment compensated load beam type of sensor that compensates for the center of the grain flow striking the sensor plate other than perpendicular to the load beam. However, U.S. Pat. No. 5,343,761 does not compensate for variations in the frictional properties of the grain except by use of a non-linear calibration for various grain types and moisture.
E.P. Patent No. 2,742,324 uses a curved sensor plate near the top of the elevator attached to a hall effect sensor or to parallel springs having strain gauges. However, it makes no provision for compensation in the frictional properties of the grain, except for a complicated calibration routine using empirical test weights, multipliers, and offsets. Furthermore, the arrangement in E.P. Patent No. 2,742,324 relies upon early contact of the grain flow with the grain mass flow sensor assembly as the grain separates from the grain elevator paddles as the grain elevator drive chain loop passes over the upper sprocket. Locating the curved sensor plate near the top of the elevator in this way is done in order to attempt to measure the grain mass flow rate before the grain flow loses its “contiguous shape,” which may or may not be accomplished, depending on the bulk properties of the grain flow. Additionally, the measuring accomplished by the sensor plate arrangement in E.P. Patent No. 2,742,324 all takes place over an arc of about 15 to 30 degrees, which limits accuracy.
E.P. Patent No. 1,169,905 provides for controlled grain flow from the exit of the grain elevator using a curved guide surface that extends from the exit of the grain elevator to the grain mass flow sensor assembly. This concentrates the grain flow, resulting in a more linear relationship between the grain mass flow rate and the mass flow sensor signal. Further, E.P. Patent No. 1,169,905 uses a curved sensor plate and a pivot point chosen in order to minimize the effects of friction and other variable bulk properties of the grain flow. The use of a counterweight is intended to minimize the effects of inclines on the signal output. However, E.P. Patent No. 1,169,905 still used a torsional sensor, which the present inventors have found to be insufficiently robust and susceptible to inaccuracy under certain conditions. Specifically, the use of a counterweight to balance the tare weight of the sensor plate tends to make the sensor mechanism heavier, so that it cannot react as quickly to changes in the force being applied to the sensor plate, and so that heavier bracketry is required to support the grain mass flow sensor assembly. Further, while a counterweight arrangement of this type may cancel out the effect of incline or slope angle, it inherently makes the output signal more susceptible to errors due to increased overall tare weight of the measurement mechanism reacting to lateral or longitudinal accelerations of the overall system, for example as the upper part of the combine moves sideways as the combine rolls back and forth about its longitudinal center of gravity over uneven ground.
Alternative methods of determining grain mass flow have been used with various levels of success without attaining to the desired level of overall accuracy. An example of such alternative method is measuring the tension of the belt driving the grain elevator itself, coupled with determining the speed of the elevator, in order to determine the mass of grain being lifted. In this arrangement, the effect of inclines upon the weight of the pulley being used to measure the tension of the belt is compensated for using a slope sensor. However, using the tension of the belt driving the grain elevator to determine the mass of grain being lifted is further susceptible to effects from the bulk properties of the grain such as friction and cohesiveness, for example as the grain elevator paddles engage the accumulated mass of grain at the bottom of the grain elevator.
What is needed in the art, therefore, is grain mass flow sensor arrangement that produces an accurate relationship between grain mass flow rate and the mass flow sensor signal over a high range of measurement and with high instantaneous accuracy. What is further needed is a grain mass flow sensor arrangement that compensates for slopes, inclines, and unevenness without adding extra tare weight to the measurement mechanism. A grain mass flow sensor arrangement is needed that functions reliably and accurately despite vibration, dust, and abrasion. What is further needed is a grain mass flow sensor arrangement that is durable for assembly and maintenance. Finally, a grain mass flow sensor arrangement is needed that measures the mass flow of grain flowing in a controlled coherent fashion, and that compensates for variable bulk properties of the grain, such as friction, crop type, bulk density, moisture, and cohesiveness, while requiring minimum calibration.